Method of forming a high friction element



other.

2,828,254 26,... Janet M2... 25, 1955s.

America, Verona, N. J.

No Drawing. Applicatioh 5,1954" 1 Serial; No. 402,402;

3 Claims. (Cl. 204-481) Our invention relates to "method of making friction elements. 1,

The generic term friction element, applies" to such devices as friction clutches and brakes,'bearings, bushings and other likearticles wherein one member slidably engages another member or wherein two bodiesin contact witlieach otherare' adapted to moveflrelative to each Certain of these devicessuch as friction clutches and 'brakes require elements with high coefficients. of friction and such elementsare;;ltereinafter'.referred to as high friction-elements;" other devicessuch'as bearings and bushings require elements with low coeflicients of friction and suclrelernents are hereinafter eferred ,to.as low friction on anti frictioirele'ments; ifi'f' ff While typical operating conditions vary withthetype of element, certain commonjproblenrs"exist. 1 For example, in order to prevent fade, freeze-up, and ,other associated phenomena, the "frictional jcoefiic'ie'nt of anyelmentideally, should be heldconstant and invparticular should be substantially independent of temperature. As,

far as is known to ,us, knofwn'elementshave frictional coefficients whose values change. sharply. with temperature. Typical operating temperatures fol-both high friction ,and low friction elements 1 have greatly increased over those used only a fewfyears ago and an urgentdemand has been created ffori frictional elements .whose frictional ccefiicientshave improved thermal stability. Moreoverfthe element itself mustbe' securely bonded to a supporting member; known bonds will rapidly dis integrate at these increased temperatures. Furthermore, the w'orking'urfsees hflgnowhelement's will deteriorate rapidly and fail under thinfluencefof thesevere thermal stresses created b y' these .tem piei atures,"

cordingly, t-1s n object o the present invention to pi ovide' improved friction'elements which obviatethese disadvantages. w i, Itis another object to provide novel methods for producing these improved elements A f rthe r object" ist okprpvide imprqvpd friction elemerits "with thermally stable fr" onal coeflicients,

Still-"a further objecltiis to prpvide a novel methodfor electrophoretically forming frictio'n' elements,- I, w Yet 'a' further "object'is to provide'a novel method for bonding'fric'tion elements to a supporting member. -A"nother "object is 'to*providef frictionelements which exhibit good resistanbe"to .Wear at high operating temperatures. j; i: i

, Ir1; our coperrding ;applicatidn, "S.1N. 386,882, filed October 19, 1953, we disclosed processesfor forming electrophoretic bath.

an adherent coating onthat electrode. Exceptional uni-. formity of coating thickness and compacting (with an attendant relatively high coating. density) are obtained as compared withdipping, spraying, brushing, andother more conventional methods of application. .Irregularly shaped objects of anydesired contour can be coated with excellent uniformity and reducibility of coating. Further details of this process will befound in the above mentioned application. 1

In the-present invention, a mixture comprising a-major.. portion by weight'of particles. of a reducible: metallic. compound and aminor. portion by .weighhof particles. of suitable friction characteristics modifying. agents is. electrophoretically codeposited on a base member of. any desired shape-and contour. The coated member then. heated to a temperature less than .the softening temperature of the compound, if necessary in a reducing.

atmosphere, to reduce the metallic compound to metal. and form a metal matrix whose interstices entrap the. par-- ticles 10f thefriction modifying agents. -The..amountsof friction modifying agent and matrix forming material. are such that the layer after reduction contains by Weight of metallic ,matrix-and 20-5% of frictionv modifying agent. As the reduction-takes place, co-diffusion between the deposited'metal and the basemember. occurs at their interface, and a strong durablebon'dnis formedgll, a I For high friction elements adapted, formexarnple, to. Withstand temperatures on the order of 2000 F., the. reducible compound for example can be oxidesv of such refractory metals as nickel, copper,--iron, chromium, ,.or alloys of thesemetals. --The friction modifying agent must have a high friction -coefiicient and can 'be, -for example, molybdenum disilicide, aluminum oxide and: the like. N Y 7 ,For low or anti-friction elements adapted, for-example, to Withstand temperatures on the order of 500 Fffthe reduciblecompounds can be of the type indicated abovebut also'can be oxides of tin, lead, silver-onthein alloys. The friction modifying agent must have a low friction coefiicient and-can be, for example, a-lubricant such as molybdenum disulfide, tungsten disulfide,- uranium disulfide, graphite and the like. 'The base member in this'type of application is genrallycomposed of various metals and alloys. -Electro receiving surface, this surface must first be treated to render it conductive before the deposition takes place,

for example, by one of the methods disclosed in our;

copending application, S. N. 398,129, filed December 14, 1953, now abandoned.

The following examples set forth certain well-defined instances of the application of this invention. They are, however, not to be considered as limitations thereof,

fromthe spirit and scope'of this invention? 5 i a I v V 0 Example I i ,A mixture containing 87% by weight of nickel oxide particles and 13% by-.weight of molybdenumdisilicide particles dispersed in isopropyl alcohol and dilutedato -au;

5% concentration in the manner outlined in the aforesaid-copending application S. N. 386,882.

This dispersion was then poured into a conventional An annular stainless steel disc /sff thigh-With an external diameter of 12f and aninter;

nal diameter of 8 was suspended in the dispersion; A

flat' stee'l plate was suspended in the dispersion in such manner that the plate surfaces and disc surfaces were sipce. many-modifications may be madewithout departing parallel. The plate-disc separation was adjusted to 2". A direct voltage of 325 volts was applied between the disc and plate with such polarity that the disc functioned as the cathode. Nickel oxide and molybdenum disilicide particles immediately began to codeposit on that surface of the disc which faced the plate. After a 45-second interval, the disc was disconnected and removed from the bath. The codeposited coating attained a thickness of 100 microns during this interval.

The disc was then fired in hydrogen at a temperature of 1475 F. for a period of 20 seconds. Subsequent cross-sectional analysis established that the nickel oxide was reduced to nickel in the form of a matrix securely bonded by coditfusion to the surface of the disc. The molybdenum disilicide particles did not enter into the reaction but were entrapped within the pores or interstices of the nickel matrix. The ratio by weight of nickel to molybdenum disilicide was found to be approximately 9 to 1.

Tests revealed tht the coefficient of friction for this coated disc was on the order of .4 and exhibited little variation as the operating temperature was increased from 70 F. to 1900" F. As the temperature increased beyond this latter value and approached the melting temperature of nickel (on the order of 2500 F.) accurate friction values could not be obtained due to structural and surface charges in the nickel. The molybdenum disilicide due to its higher melting temperature (on the order of 3400 F.) retained its initial structural characteristics.

By repeating the deposition and firing process as many times as necessary, it was found that coating thicknesses up to 3000 microns and higher could be built up on the disc.

The above process was repeated with different firing temperatures and different weight percentages for the nickel oxide and molybdenum disilicide. When the percentage by weight of the molybdenum disilicide was too large, on the order of 20%, the nickel matrix was too weak and not well bonded to the disc and the entire coating tended to disintegrate into powder. Best results were obtained by maintaining the percentage by weight of nickel within the range 8095%. All firing temperatures falling within the range 1300-l800 F. were found to be satisfactory.

When the discs prepared in this manner were tested in a disc friction clutch, it was noted that there was a tendency at high temperatures for the discs to freeze. Therefore, a small amount, on the order of 1% by weight, of molybdenum disulfide was added to the nickel oxide-molybdenum disilicide dispersion and the disc was then prepared as outlined above. The lubricating action of the disulfide was found sufficient to prevent freezing. While molybdenum disulfide normally oxidizes at relatively low temperatures, the quantity is so small in comparison to the other materials that whatever oxidation does take place does not adversely affect the operation.

If higher oxidation temperatures are required, a like amount of tungsten disulfide can be substituted for the molybdenum disulfide.

Example II A gross dispersion containing 85% by weight of copper oxide particles and by weight of aluminum oxide was immersed in isopropyl alcohol and diluted to a 5% concentration.

This dispersion was then poured into a conventional electrophoretic bath. A steel disc /2" thick with a diameter of 5" was suspended in the dispersion. A flat steel plate was suspended in the dispersion in such manner that the plate surfaces and disc surfaces were parallel. The plate-disc separation was adjusted to 2 /2". A direct voltage of 500 volts was applied between the disc and plate with such polarity that the disc functioned as the cathode. Copper oxide and aluminum oxide par- 4 ticles immediately began to codeposit on that surface of the disc which faced the plate. After a 50 second interval, the disc was disconnected and removed from the bath. The codeposited coating attained a thickness of microns during this interval.

The disc was then fired in hydrogen at a temperature of 1300 F. for a period of 25 seconds. Subsequent cross-sectional analysis established that the copper oxide was reduced to copper in the form of a matrix securely bonded by codiifusion to the surface of the disc. The aluminum oxide particles did not enter into the reaction but were entrapped within the interstices of the copper matrix. The ratio by weight of copper to aluminum was found to be approximately 9 to 1.

Tests revealed that the coeflicient of friction for this coated disc was on the order of .55 and exhibited little variation as the operating temperature was increased from 70 F. to 1400 F. As the temperature increased beyond this latter value and approached the melting temperature of copper (on the order of 1900 F.), accurate friction values could not be obtained due to structural and surface changes in the copper. The aluminum oxide, due to its higher melting temperatures, retained its initial structural charcteristics.

The coating thickness can be built up in the same manner as set forth in Example I. The firing temperatures and the weight percentages of the copper oxide-aluminum oxide mixture were varied in the same manner as Example I with substantially the same results.

Example III A mixture comprising about 86% by weight silver oxide particles, about 6% by weight of copper oxide particles and about 8% by weight of molybdenum disulfide particles was ball milled for a period of from to 200 hours in 5% concentration in a medium of 50% by weight of glycerine and 50% by weight of isopropyl alcohol. The resulting dispersion was activated by continuous agitation for a period of about one hour.

This dispersion was then poured into a conventional electrophoretic bath. A steel sleeve 6 in length and having an internal diameter of 2" was suspended in the dispersion. A steel rod 6" in length and having a diameter of A" was suspended in the dispersion in such manner that the axis of the rod coincided with the axis of the sleeve. A direct voltage of 250 volts was applied between the sleeve and rod with such polarity that the sleeve functioned as the cathode. The silver oxide-copper oxide-molybdenum sulfide particles immediately began to deposit uniformly on the internal surface of the sleeve. After a 55 second interval, the sleeve was disconnected and removed from the bath. The deposited coating attained a thickness of 90 microns during this interval.

The coated sleeve was then fired in hydrogen at a temperature of 1300 F. for a period of 15 seconds. Subsequent cross-sectional analysis revealed that a silvercopper matrix was formed and bonded to the sleeve. The molybdenum disulfide was entrapped within the interstices of the matrix. The disulfide, due to the presence of hydrogen, was not oxidized to any appreciable extent during the firing operation. The weight composition of the reduced coating was about 85% silver, 5% copper and 10% molybdenum disulfide.

Tests revealed that the coefiicient of friction for the sleeve was on the order of .10 and exhibited little vairiation as the operating temperature was increased from 70 F. to 500 F. As the temperature increased beyond this latter value, matrix began to soften and separate from the sleeve.

The coating thickness can be built up in the same I manner as set forth in Example I. This experiment was by maintaining the percentage by weight of molybdenum disulfide between the limits of 5 to Example IV Example III was repeated using an initial mixture of lead oxide, tin oxide, copper oxide and graphite particles. After electrophoretic deposition of the particles and subsequent firing at a temperature of 800 F. for a period of 30 seconds, a matrix of a lead-tin-copper alloy containing entrapped graphite was formed having a composition by Weight of 78.4% lead, 9.0% tin, 2.6% copper and 10% graphite.

The coefficient of friction of this sleeve was found to be on the order of .1 over the same general range as Example III. Increasing the percentage of graphite decreases the coeflficient of friction but also weakens the matrix structure so that best results are obtained by maintaining the percentage by weight of graphite within the range 5-15%.

Although in the above examples, we have indicated certain definite firing temperatures, duration of reactions, types of materials, coefl'icients of friction, etc., it is to be understood that any or all of these can be varied widely within the scope of our invention, since the particular conditions of operation are governed largely by the specific end structure desired. For example, the firing temperature must be high enough to perform the desired reduction and low enough to prevent softening or melting of the materialsused. The actual temperature used will vary depending on the characteristics of these materials.

Therefore, it is apparent that many widely different embodiments of this invention can be made without departing from the spirit and scope thereof and we do not intend to be limited except as indicated in the appended claims.

What is claimed is:

1. The method of forming a high friction element which comprises the steps of electrophoretically depositing a particle mixture having a metallic matrix forming material of the group consisting of nickel oxide and. copper oxide, and a friction material of the group consisting 6, of molybdenum disilicide and alumina out of an organic medium upon a selected surface of a metallic base member, the amount of said matrix forming material and friction material producing a layer having -95% by Weight of metallic matrix and 20-5% of friction material, and heating said member in a reducing atmosphere at a temperature to reduce said matrix forming material to form a metallic matrix bonded to said member Whose interstices are filled with said friction material, Without reducing said friction material.

2. The method of claim 1 in which the matrix forming material is copper oxide, the friction material is alumium oxide, and the member is heated in a hydrogen atmosphere to reduce said copper oxide to copper.

3. The method of forming a high friction element which comprises the steps of electrophoretically depositing a particle mixture having a composition of 80 to by weight of nickel oxide, 20 to 5% by weight of molybdenum disilicide, and about 1% by weight of molybdenum disulfide out of an organic media upon a selected surface of a metallic base member; and heating said member to a temperature within the range 1300- 1800 F. in a hydrogen atmosphere until said nickel oxide is reduced to nickel whereby a nickel matrix is formed which is bonded to said member and whose interstices are filled with said disilicide and said disulfide particles.

References Cited in the file of this patent 

1. THE METHOD OF FORMING A HIGH FRICTION ELEMENT WHICH COMPRISES THE STEPS OF ELECTROPHORETICALLY DEPOSITING A PARTICLE MIXTURE HAVING A METALLIC MATRIX FORMING MATERIAL OF THE GROUP CONSISTING OF NICKEL OXIDE AND COPPER OXIDE, AND A FRICTION MATERIAL OF THE GROUP CONSISTING OF MOLYBDENUM DISILICIDE AND ALUMINA OUT OF AN ORGANIC MEDIUM UPON A SELECTED SURFACE OF A METALLIC BASE MEMBER, THE AMOUNT OF SAID MATRIX FORMING MATERIAL AND FRICTION MATERIAL PRODUCING A LAYER HAVING 80-95% BY WEIGHT OF METALLIC MATRIX AND 20-5% OF FRICTION MATERIAL, AND HEATING SAID MEMBER IN A REDUCING ATMOSPHERE AT A TEMPERATURE TO REDUCE SAID MATRIX FORMING MATERIAL TO FORM A METALLIC MATRIX BONDED TO SAID MEMBER WHOSE INTERSTICES ARE FILLED WITH SAID FRICTION MATERIAL, WITHOUT REDUCING SAID FRICTION MATERIAL. 